HETE observations of the gamma-ray burst GRB 030329: Evidence for an underlying soft X-ray component

An exceptionally intense gamma-ray burst, GRB 030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11: 37: 14 UT on 2003 March 29. The burst consisted of two similar to10 s pulses of roughly equal brightness and an X-ray tail lasting more than 100 s. The energy fluence in the 30-400 keV energy band was S-gamma 1.2 x 10(-4) ergs cm(-2), making GRB 030329 one of the brightest GRBs ever detected. Communication of a 20 error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, and radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst light curves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB; the 2-10 keV fluence of this component is similar to7 x 10(-6) ergs cm(-2). The main pulses of GRB 030329 were preceded by two soft, faint, nonthermal bumps. We present details of the HETE observations of GRB 030329.